Fuel cell separator and method for manufacturing the same

ABSTRACT

A fuel cell separator  60  having a metal plate and an anticorrosion resin coating layer  55  formed thereon is provided, with which adhesion between the resin coating layer  55  and its counterpart member is further increased and the durability of a fuel cell unit is improved. In forming the fuel cell separator  60  having a separator substrate  50  that is a metal plate and an anticorrosion resin coating layer  55  formed thereon, the resin coating layer  55  is formed such that it has a surface roughness Ra of 0.5 to 13.5 μm. Increasing the surface roughness will produce an anchoring effect, which will improve the adhesive force at the interface. The aforementioned surface roughness Ra can be obtained either with the use of fillers that are mixed into the resin coating layer  55  or with external force applied to the surface of the resin coating layer  55  by means of shot blasting, for example.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell separator and a method formanufacturing the same.

2. Background Art

As typical examples of fuel cells, polymer electrolyte fuel cells areknown. FIG. 7 is a cross-sectional view illustrating an example of sucha fuel cell, in which a membrane electrode assembly 3 having anelectrolyte membrane 1 and a pair of electrode layers 2 each of whichhas a sequential stack of a catalyst layer 21 and a diffusion layer 22and is formed on each side of the electrolyte membrane 1 is provided,and the opposite sides of the membrane electrode assembly 3 aresandwiched between separators 5,5 each having gas flow channels 4,whereby a single fuel cell unit is formed. An electrolyte membrane 1 aprotrudes beyond the periphery of the electrode layers 2, and a spacebetween the protruding electrolyte membrane 1 a and the separators 5 isfilled with a gasket 6 as an adhesive having a sealing function in sucha manner that all of the members are integrated, whereby sealing betweenthe two electrode layers 2,2 is ensured. Though not shown, a resin framemay be disposed between the gasket 6 and the separator 5 in some cases.In such a case, an adhesive is further applied between the resin frameand the separator so that they are integrated.

In order for a fuel cell unit to exhibit excellent power generationperformance over a long period of time, the durability of the sealbetween the gasket and the separator or between the resin frame and theseparator can be an important factor. However, since product water thatwill be produced by a power generation reaction contains acids, fluorineions, and the like, such product water containing acids, fluorine ions,and the like could cause the bonding interface between the gasket 6 andthe separator 5 or the bonding interface between the resin frame and theseparator to deteriorate, thus failing to ensure seal durability. In anextreme case, the separator could become corroded due to the influenceof the product water.

In order to avoid the aforementioned problem, Reference 1 (JP PatentPublication (Kokai) No. 2007-12300 A) discloses a fuel cell separator inwhich an anticorrosion resin coating layer is formed on part of thesurface of the separator (a region corresponding to a non-powergenerating region of the surface of the separator). With such a resincoating layer formed, the anticorrosive effect of the separator can beincreased. In addition, when a seal member such as an adhesive or agasket is disposed on the separator with the resin coating layerinterposed therebetween, seal durability would also be ensured. Theresin coating layer is formed by, for example, electrodepositing acationic resin, which has been obtained by ionizing resin powder such asepoxy resin, urethane resin, acrylic resin, or polyimide resin, on thesurface of the separator.

As another example of a fuel cell separator that solves the sametechnical problem, Reference 2 (JP Patent Publication (Kokai) No.2007-242576 A) discloses a fuel cell separator and a method formanufacturing the same, in which cathodic electrolysis in an alkalinesolution is applied to a surface of a peripheral portion of a separatormade of stainless steel, excluding gas flow channels (a conductingsection), so that a hydrated iron oxide film is formed on the surface ofthe peripheral portion of the separator, and further, a resin sheetlayer made of an aqueous electrodeposition resin is electrodeposited onthe hydrated iron oxide film. Examples of such aqueous electrodepositionresins include amine resins.

Hydrophilic aqueous resins are environmentally friendly materials andare often used as materials of resin coating layers. However, since aseparator made of stainless steel has a surface on which a passive filmmade of a chromium oxide layer is formed, the separator has low affinityfor hydrophilic aqueous resins. Thus, when a resin sheet layer made ofan aqueous electrodeposition resin is directly formed on the surface ofthe separator made of stainless steel, the resin would have low adhesionto the separator and thus could easily peel off the separator. Thus,when a hydrated iron oxide film is formed at the interface between thesurface of the separator made of stainless steel and the resin coatinglayer as described in Reference 2, adhesion between the separator andthe resin coating layer increases, whereby a fuel cell separator withhigh corrosion resistance and increased durability can be provided.

SUMMARY OF THE INVENTION

The inventors have conducted continuous studies and experiments on fuelcell units that employ fuel cell separators including the aforementionedanticorrosion resin coating layer as parts of the components of theseparators. They found that although a dense, uniform resin coatinglayer can be obtained through electrodeposition of a resin coating layeron the surface of a metal separator, there is a limitation in adhesiveforce obtained between the resin coating layer and its counterpartmember; for example, adhesive force between the resin coating layer anda resin frame or between the resin coating layer and a gasket. This isbecause the surface planarity of the resin coating layer is extremelyhigh. Thus, they learned that that there is still room for improvementof design of fuel cell units in order that fuel cell units with highpower generation performance and high durability that are expected to beachieved in the future can be provided.

The present invention has been made based on the aforementionedexperience. It is an object of the present invention to provide a fuelcell separator and a method for manufacturing the same, in which thefuel cell separator has a metal plate and an anticorrosion resin coatinglayer formed thereon, and adhesion between the resin coating layer andits counterpart member (for example, adhesion between the resin coatinglayer and a resin frame or between the resin coating layer and a gasket)is further increased, whereby the power generation performance anddurability of a fuel cell unit to be manufactured are further increased.

A fuel cell separator of the present invention is a fuel cell separatorincluding a metal plate and an anticorrosion resin coating layer formedthereon, in which the surface roughness Ra of the resin coating layer is0.5 to 13.5 μm. In the present invention, the surface roughness Rarefers to the center-line mean roughness; that is, the mean value ofprofile peak heights and valley depths from the centerline.

When the resin coating layer has the aforementioned surface roughness,an anchoring effect is produced at the interface between the stackedlayers, whereby adhesion between the resin coating layer and itscounterpart member (for example, adhesion between the resin coatinglayer and a resin frame or between the resin coating layer and a gasket)would be increased, compared to a case in which the surface of the resincoating layer is flat. Thus, a fuel cell unit constructed with the fuelcell separator of the present invention can have high durability withlittle possibility of delamination or the like.

As will be described in the “example” section, when the surfaceroughness Ra of the resin coating layer is less than 0.5 μm, theinterface between the stacked layers cannot have a sufficient anchoringeffect. Thus, a significant increase in adhesive force will not occur.Meanwhile, a surface roughness Ra of greater than 13.5 μm is notpreferable because such roughness could result in gas leakage from theinterface between the stacked layers.

In one embodiment of the fuel cell separator of the present invention,the aforementioned resin coating layer includes fillers, and theaforementioned surface roughness Ra is provided by the presence of thefillers. Exemplary materials of fillers include acrylic resin particles,polyester resin particles, epoxy resin particles, and urethane resinparticles. The volume mean particle diameter of the fillers ispreferably about 50 to 100 nm. When the volume mean particle diameter ofthe fillers is less than 50 nm, it is difficult for the resin coatinglayer to have a surface roughness Ra of greater than or equal to 0.5 μm.Meanwhile, when the volume mean particle diameter of the fillers is over100 nm, the resin coating layer will be likely to have a surfaceroughness Ra of over 13.5 μm. Exemplary fillers, which are preferable interms of easy availability and dispersion properties, are acrylic resinparticles with a volume mean particle diameter of 50 to 100 nm. Notethat the volume mean particle diameter can be determined with a laserlight scattering method.

In another embodiment of the fuel cell separator of the presentinvention, the surface roughness Ra is imparted as a result ofroughening treatment applied to the surface of the resin coating layerformed. Examples of roughening treatment to be applied include shotblasting, plasma treatment, corona treatment, and liquid honing.

A method for manufacturing a fuel cell separator according to one aspectof the present invention is a method for manufacturing a fuel cellseparator in which an anticorrosion resin coating layer is formed on ametal plate, the method including at least a step of electrodepositingfillers and an aqueous resin included in an electrocoating material, inwhich the content of the fillers is greater than or equal to 10 mass %,on part of the surface of the metal plate, thereby forming a resincoating layer with a surface roughness Ra of 0.5 to 13.5 μm.

Materials, volume mean particle diameter, and the like of the fillerscan be the same as those given as examples in the description of a fuelcell separator earlier. Preferably, an electrocoating material thatincludes acrylic resin particles with a volume mean particle diameter of50 to 100 nm as fillers is used.

As described above, when electrodeposition coating is performed with theuse of an electrocoating material including fillers, it is possible toform a dense, uniform resin coating layer and impart a desired roughnessRa to the surface of the resin coating layer formed.

A method for manufacturing a fuel cell separator according to anotheraspect of the present invention is a method for manufacturing a fuelcell separator in which an anticorrosion resin coating layer is formedon a metal plate, the method including at least the following steps:forming a resin coating layer by electrodepositing an aqueous resinincluded in an electrocoating material on part of the surface of themetal plate, and applying roughening treatment to the surface of thethus formed resin coating layer with external force so as to impart asurface roughness Ra of 0.5 to 13.5 μm.

Examples of roughening treatment to be applied include shot blasting,plasma treatment, corona treatment, and liquid honing. Among such formsof treatment, shot blasting is preferable in terms of ease of treatment.In shot blasting, a metal plate (separator) having a resin coating layerformed on its surface is appropriately masked and the surface of theresin coating layer is blasted with particles (media) of alumina, TiC,or the like with a particle diameter of, for example, 5 to 50 μm,whereby a desired surface roughness can be imparted to the surface ofthe resin coating layer.

According to the present invention, an improved fuel cell separator isprovided, which has a metal plate and an anticorrosion resin coatinglayer formed thereon and which has high corrosion resistance and iscapable of ensuring high seal durability over a long period of time whenbuilt into a fuel cell unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views for illustrating the steps of manufacturing afuel cell separator of the present invention;

FIG. 2 is a schematic view for illustrating an embodiment in which aresin coating layer of a fuel cell separator of the present invention isformed by electrodeposition coating;

FIGS. 3A and 3B are schematic partial enlarged views of fuel cell unitsin which a prior-art fuel cell separator is used and in which a fuelcell separator of the present invention is used, respectively;

FIG. 4 is a schematic view illustrating an aspect of bonding between aseparator substrate and a resin coating layer according to anotherembodiment of a fuel cell separator of the present invention;

FIG. 5 is a graph showing the relationship between the resin surfaceroughness (Ra) and adhesive force according to Embodiment 1;

FIG. 6 is a graph showing the relationship between the content offillers and resin surface roughness (Ra) according to Embodiment 2; and

FIG. 7 is a schematic view for illustrating a fuel cell unit.

DESCRIPTION OF SYMBOLS

-   50 separator substrate-   55 anticorrosion resin coating layer-   55 a resin coating layer with increased surface roughness-   60 separator with a resin coating layer-   61 resin frame-   62 adhesive layer-   63 gasket

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings.

FIGS. 1A to 1C are views for illustrating an embodiment of a fuel cellseparator according to the present invention. As shown in FIG. 1A, ametal plate is used as a separator substrate 50. Examples of metalplates include, but are not limited to, plates made of austeniticstainless steel such as SUS304, SUS305, SUS310, SUS 316, and SUSMX7; andplates made of ferritic stainless steel such as SUS430. In addition,titanium, iron, aluminum, and the like can also be used.

Feed communication holes 51 a, 51 b, and 51 c through which fuel gas,oxidant gas, and cooling water are fed, and discharge communicationholes 52 a, 52 b, and 52 c through which the fuel gas, oxidant gas, andcooling water are discharged are provided at the opposite ends of theseparator substrate 50. Further, the separator substrate 50 is providedwith gas flow channels 53 with projecting/recessed groove patterns,through which supplied fuel gas or oxidant gas flows. A region in whichthe gas flow channels 53 are provided is a conducting section positionedopposite a power-generation section of a membrane electrode assembly.

In this embodiment, an anticorrosion resin coating layer 55 is providedin regions except for the conducting section of the separator substrate50. In the illustration, the resin coating layer 55 is formed throughelectrodeposition coating of an ionized aqueous resin as shown in theschematic view of FIG. 2. However, the method of forming the resincoating layer 55 is not limited thereto. In the example shown in FIG. 2,a negative voltage is applied to the separator substrate 50 with amasked conducting section and a positive voltage is applied to a counterelectrode 70, in a solution containing aqueous resins (NH⁺-resins) 110that have been obtained by ionizing a portion of the resin powder withNH⁺, for example. Accordingly, the aqueous resins 110 are drawn to anunmasked region of the separator substrate 50, thereby bonding to thesurface thereof. By such electrodeposition coating, the resin coatinglayer 55, which is dense and uniform and has a flat surface, is formedon the surface of the separator substrate 50, except for at the maskedregion, as shown in FIG. 1B. If necessary, baking treatment at about 150to 250° C., or desirably about 200° C. can be applied to the resincoating layer 55 so that the resin coating layer 55 can be formed in adenser and more uniform manner. Examples of such aqueous resins includeepoxy resins, urethane resins, acrylic resins, and polyimide resins.

FIG. 3A is a partial schematic view of a fuel cell unit that is formedusing a separator 60 having the thus formed resin coating layer 55. InFIG. 3A, reference numeral 61 denotes a resin frame disposed between amembrane electrode assembly (not shown) and the separator 60. The resinframe 61 and the separator 60 are bonded so as to be integrated witheach other with an adhesive layer 62 interposed therebetween. Referencenumeral 63 denotes an example of a gasket used to ensure sealingproperties in construction of a fuel cell unit. As shown, the surface ofthe resin coating layer 55 formed by electrodeposition coating is flat.Thus, there is a possibility that adhesion at the bonding interfacebetween the resin coating layer 55 and its counterpart member (in theillustration, the bonding interface between the resin coating layer 55and the adhesive layer 62 interposed between the resin frame 61 andseparator 60, and the bonding interface between the resin coating layer55 and the gasket 63) may be insufficient. In that case, shear stresscould be generated at each bonding interface, causing interfacialdelamination, due to the repeated cooling/heating cycles in the courseof the use of the fuel cell unit, for example.

In order to avoid such a circumstance, according to one embodiment of aseparator of the present invention, roughening treatment is applied tothe surface of the resin coating layer 55 formed by electrodepositioncoating, so that a surface roughness Ra of 0.5 to 13.5 μm is imparted tothe surface. Examples of roughening treatment include so-called shotblasting in which the target surface is blasted with metal particles orthe like. FIG. 1C shows a separator 60 that has been subjected toroughening treatment. Thus, a resin coating layer 55 a with increasedsurface roughness is obtained.

FIG. 3B is a view corresponding to FIG. 3A, in a case in which theseparator 60 that has been subjected to roughening treatment is used.Since the surface of the resin coating layer 55 a has desiredprojections and recessions, it has an increased area for bonding to thecounterpart member, and thus it has increased adhesion response pointswith the aid of intermolecular bonds. Further, since an anchoring effectis produced, the adhesive force between the two layers is significantlyincreased. Accordingly, adhesion at the bonding interface issignificantly increased, whereby peeling that would occur at the bondinginterface is suppressed and the durability of the fuel cell unit issignificantly increased.

When shot blasting is applied as roughening treatment to the surface ofthe resin coating layer, the surface roughness to be obtained can beappropriately changed with appropriate control of the pressure, time,and type of blasting media used. As other examples of rougheningtreatment, it is also possible to apply plasma treatment, coronatreatment, liquid honing, or the like. In the case of plasma treatmentor corona treatment, for example, a desired surface roughness can beobtained with appropriate control of the current, time, interelectrodedistance, and the like, while in the case of liquid honing, a desiredsurface roughness can be obtained with appropriate control of thepressure, time, type of honing media, and the like.

According to an alternative embodiment of a separator and a method formanufacturing the same of the present invention, an electrocoatingmaterial including fillers, which are capable of taking on aqueousproperties by being ionized with an appropriate means, is used inperforming electrodeposition coating. For the fillers, those mentionedearlier are preferably used. The resin included in the electrocoatingmaterial can also be the same as that mentioned earlier. Whenelectrodeposition coating is performed with such an electrocoatingmaterial in a manner similar to that described with reference to FIG. 2,it is possible to form a separator having a resin coating layer with asurface roughness Ra of 0.5 to 13.5 μm without the need to apply theaforementioned roughening treatment following the electrodepositioncoating. As will be described in the “example” section, the content ofthe fillers has a substantially proportional relationship to the surfaceroughness Ra of the resin coating layer 55 formed. However, when thecontent of the fillers is less than 10 mass %, it is impossible to formthe resin coating layer 55 with a surface roughness Ra that is greaterthan or equal to 0.5 μm.

When electrodeposition coating is performed with the use of anelectrocoating material including fillers, it is possible to change thesurface roughness of the resin coating layer as desired not only bycontrolling the content of fillers but also by retarding the speed ofstirring a coating material or the speed of thermally curing the resincoating layer, for example.

Next, a variation in which stainless steel is used as the separatorsubstrate 50 will be described with reference to FIG. 4. When theseparator substrate 50 is stainless steel, a passive film 56 made of achromium oxide film is deposited on the surface of the separatorsubstrate 50 as shown in FIG. 4. When the resin coating layer 55 is tobe formed with the use of an aqueous resin as an environmentallyfriendly material, there is a possibility that the resin could peel offthe passive film 56 due to thermal expansion or the like that wouldoccur during the use of the fuel cell unit, because the passive film 56has low affinity for aqueous resins and thus has low adhesive force. Inorder to avoid such a circumstance, cathodic electrolytic treatment inan alkaline solution is applied in advance to a region of the separatorsubstrate 50 on which the resin coating layer 55 is to be formed, sothat a hydrated iron oxide film 57 is formed. Further, wet treatmentwith water is applied to the surface of the thus formed hydrated ironoxide film 57, so that a water-treated layer 58 is formed. Then, anaqueous resin is electrodeposited on the hydrated iron oxide film thathas been subjected to the wet treatment with water, whereby the resincoating layer 55 is formed.

In the aforementioned case, the alkaline solution used is anelectrolytic treatment solution. For example, a 5 to 50 mass % sodiumhydroxide solution is used, or an aqueous solution obtained by adding0.2 to 20 mass % trisodium phosphate, 12-hydrate or 0.2 to 20 mass %sodium carbonate as a buffering agent to a 5 to 50 mass % sodiumhydroxide solution is used. The treatment is applied under theconditions of, for example, a liquid temperature of 20 to 95° C., acurrent density of greater than or equal to 0.5 A/dM², and a processingtime that is greater than or equal to 10 seconds.

In the aforementioned separator, the hydrated iron oxide film 57 formedby cathodic electrolytic treatment in an alkaline solution is depositedon the passive film 56 that is present on the surface of the separatorsubstrate 50 made of stainless steel. Thus, the separator substrate thathas been subjected to the electrolytic treatment can maintain thecorrosion resistance of the separator substrate before being subjectedto electrolytic treatment. Further, since the hydrated iron oxide film57 and the passive film 56 on the separator substrate 50 are similar incomposition, they have a high degree of adhesion to each other with theaid of metallic bonding. In addition, when the surface of the hydratediron oxide film 57 is subjected to water treatment to form thewater-treated layer 58, wettability of the surface of the hydrated ironoxide film 57 with an electrocoating material will be increased, wherebyan aqueous resin is uniformly electrodeposited on the surface of thehydrated iron oxide film 57 and generation of pin holes can thus besuppressed. Further, the hydrated iron oxide film 57 can be bonded to ahydrophilic functional group of an aqueous resin that forms the upperresin coating layer 55 by, for example, hydrogen bonding. Thus, a highdegree of adhesion between the hydrated iron oxide film 57 and the resincoating layer 55 is possible.

In the aforementioned manufacturing method, the method of imparting adesired surface roughness Ra to the surface of the resin coating layer55 formed by electrodeposition coating can be either one of theaforementioned method of applying roughening treatment to the surface ofthe resin coating layer 55 with external force or the method in which anelectrocoating material including desired fillers is used. In addition,the water used is desirably ion-exchange water, and the aqueous resinused is desirably a polyamide resin. A polyamide resin has an amidegroup and/or an imide group that are/is a hydrophilic functionalgroup(s). Thus, it has high affinity for the hydrated iron oxide film 57formed on the separator substrate 50. As a result, it has a high degreeof adhesion to the hydrated iron oxide film 57 formed on the separatorsubstrate 50. In particular, since the hydrated iron oxide film 57formed on the separator substrate 50 has a mixed composition ofhydroxide and oxide of iron, a number of hydroxyl groups and the likethat are capable of bonding to an amide group and/or an imide group of apolyamide resin exist in a scattered manner on the surface of thehydrated iron oxide film 57. Thus, an electrocoating material includinga polyamide resin as an aqueous resin can have high affinity for thehydrated iron oxide film 57 formed on the separator substrate 50,whereby the resin coating layer 55 with a uniform thickness can beformed.

In the separator formed in the aforementioned manner, bonding strengthbetween each of the layers of the separator can be further increased.Thus, durability of a fuel cell unit to be formed can be furtherincreased.

EXAMPLES

A fuel cell separator of the present invention will be described withreference to examples below. It should be appreciated that presentinvention is not limited to the following examples unless it otherwisedeparts from the sprit and scope thereof.

Example 1

A region of gas flow channels (a conducting section) of a separatorsubstrate made of austenitic stainless steel SUS was masked. With themasked separator substrate as a negative electrode and with a plate madeof ferritic stainless steel SUS 430 as a positive electrode, the maskedseparator substrate was immersed in an electrodeposition bath containinga 20 mass % cationic electrocoating material (insuleed 4200: a productof Nippon Paint Co., Ltd.) that includes an aqueous polyamide imideresin, with the following conditions: a coating ratio of +/−electrodesof −1/2, an interelectrode distance of 15 cm, and a liquid temperatureof 30° C. The voltage applied was gradually increased such that thevoltage reached a predetermined level in five seconds. After havingreached the predetermined level, the applied voltage was maintained for115 to 145 seconds, so that cationic electrodeposition coating wasperformed. Then, the masking material was removed and baking at 200° C.was performed for 30 minutes, whereby a separator A with a resin coatinglayer formed was obtained. The surface roughness Ra of the thus obtainedresin coating layer of the separator A was measured with a surfaceroughness meter (Surftest SJ-201: a product of Mitutoyo Corporation) andit was found to be 0.2 μm.

Three separators A each having the aforementioned resin coating layerwere prepared, and the surface of each resin coating layer was subjectedto surface roughness treatment through shot blasting, so that separatorsB, C, and D having mean surface roughnesses Ra of 0.5 μm, 1.0 μm, and1.5 μm, respectively, were obtained. Note that adjustment of the surfaceroughness through shot blasting was accomplished with the control ofshot pressure.

As an adhesive, a thermosetting silicon resin was bonded to the surfaceof each of the resin coating layers of the separator A and theseparators B, C, and D that had been subjected to the surface roughnesstreatment. After the silicon resin had been bonded, it was left intactfor 24 hours and then a T-peel test of the bonding interface wasperformed by means of a tensile strength test. The surface roughness wasmeasured with a surface roughness meter (Surftest SJ-400: a product ofMitutoyo Corporation). FIG. 5 is a graph showing the test result. Asshown in the graph of FIG. 5, the surface roughness Ra of the resincoating layer that has not been subjected to surface rougheningtreatment is as low as 0.2 μm and the adhesive force thereof is about 3N/cm², since an anchoring effect does not act on the bonding interface,whereas the resin coating layers, each of which has a surface roughnessRa that is greater than or equal to 0.5 μm as a result of having beensubjected to the surface roughening treatment, have adhesive forcesgreater than or equal to the integral multiple of that of a resincoating layer that had not been subjected to surface rougheningtreatment.

Example 2

A region of gas flow channels (a conducting section) of a separatorsubstrate made of austenitic stainless steel SUS was masked. With themasked separator substrate as a negative electrode and with a plate madeof ferritic stainless steel SUS 430 as a positive electrode, the maskedseparator substrate was immersed in three kinds of electrodepositionbaths each containing a 20 mass % cationic electrocoating material(insuleed 4200: a product of Nippon Paint Co., Ltd.) that includes anaqueous polyamide imide resin, to which acrylic resin particles with avolume mean particle diameter of 50 to 100 nm accounting for 5 mass %,10 mass %, and 15 mass %, respectively, were added as fillers, with thefollowing conditions: a coating ratio of +/−electrodes of −1/2, aninterelectrode distance of 15 cm, and a liquid temperature of 30° C. Thevoltage applied was gradually increased such that the voltage reached apredetermined level in five seconds. After having reached thepredetermined level, the applied voltage was maintained for 115 to 145seconds, so that cationic electrodeposition coating was performed. Then,the masking material was removed and baking at 200° C. was performed for30 minutes, whereby three kinds of separators E, F, and G with resincoating layers formed were obtained.

The surface roughnesses Ra of the resin coating layers of the separatorsubstrates E, F, and G were measured with a surface roughness meter(Surftest SJ-201: a product of Mitutoyo Corporation). The graph of FIG.6 shows the results. As shown in the graph, the roughness Ra of theresin surface of the separator substrate E with a filler content of 5mass % is about 0.3 μm, the roughness Ra of the resin surface of theseparator substrate F with a filler content of 10 mass % is over 0.5 μm,and the roughness Ra of the resin surface of the separator substrate Gwith a filler content of 15 mass % is about 0.8 μm.

The aforementioned test results can confirm that controlling the contentof fillers in an electrocoating material will make it possible tocontrol the surface roughness Ra of a resin coating layer obtainedthrough electrodeposition coating, and that using an electrocoatingmaterial including fillers in amounts greater than or equal to 10 mass %can provide a resin coating layer with a surface roughness of greaterthan or equal to 0.5 μm.

It is estimated that when a thermosetting silicon resin is bonded toeach of the surfaces of the resin coating layers of the thus formedseparator substrates F and G in a similar manner as that described inExample 1, adhesive force that is substantially equal to those of theseparators B, C, and D that have been subjected to surface rougheningtreatment in Example 1 can be obtained.

[Industrial Applicability]

A fuel cell separator and a method for manufacturing the same of thepresent invention can be used for any applications of the field of fuelcells. In particular, the present invention can be advantageouslyapplied to polymer electrolyte fuel cells of vehicles.

What is claimed is:
 1. A fuel cell separator, comprising: a separatorsubstrate made of a metal plate; and an anticorrosion resin coatinglayer formed thereon, wherein the resin coating layer is formed on aportion excluding a conducting section of the separator substrate,wherein the resin coating layer has a first surface and a secondsurface, the first surface of the resin coating layer facing away fromthe separator substrate, and the second surface of the resin coatinglayer facing toward the separator substrate, and wherein the firstsurface of the resin coating layer has a surface roughness Ra, and thesurface roughness Ra is 0.5 to 13.5 μm, and the second surface of theresin coating layer is substantially flat.
 2. The fuel cell separatoraccording to claim 1, wherein the resin coating layer includes fillers,and the surface roughness Ra is provided by the presence of the fillers.3. The fuel cell separator according to claim 2, wherein the fillers areacrylic resin particles each with a particle diameter of 50 to 100 nm.4. The fuel cell separator according to claim 1, wherein the surfaceroughness Ra is provided by roughening treatment applied to a surface ofthe resin coating layer formed.
 5. The fuel cell unit comprising amembrane electrode assembly sandwiched between the fuel cell separatorsaccording to claim
 1. 6. The fuel cell separator according to claim 2,wherein an electrocoating material including acrylic resin particleseach with a particle diameter of 50 to 100 nm as fillers is used as theelectrocoating material.
 7. The fuel cell separator according to claim6, wherein a content of the fillers in the electrocoating material isgreater than or equal to 10 mass %.
 8. The fuel cell separator accordingto claim 1, further comprising: a hydrated metal oxide layer disposed onthe metal plate; and a water-treated layer disposed on the hydratedmetal oxide layer; wherein the anticorrosion resin coating layer isformed on the water-treated layer.
 9. The fuel cell separator accordingto claim 1, wherein the first surface having the surface roughness Ra isconfigured to adhere to an adhesive layer or a gasket.